A. In subjects without known organic heart disease, supraventricular arrhythmias (SVA) precipitated by exercise or occurring during routine activity increase in frequency and complexity with age and cause substantia cardiac morbidity. Although increased echocardiographic left ventricular (LV) mass predicts a higher prevalence and complexity of ventricular arrhythmias (VA) on ambulatory ECG, whether such a relationship exists between LV anatomy and exercise-induced SVA (EISVA) is unknown. We therefore examined this question in 288 healthy BLSA volunteers 20-90 years old who underwent both M-mode echocardiography and maximal treadmill exercise testing. Simple, i.e. isolated, EISVA occurred in 52 subjects (18%) and complex EISVA (comparing r 10% of beats in any minute or occurrin in runs) in 20 subjects (7%). Although univariate predictors of any EISVA were greater LV mass (p<.004), older age (<.0001), lower peak heart rate (p<.0001) and shorter exercise duration (p<.01), only age (p<.001) independently predicted EISVA by multiple logistic regression analysis. B. Although respiratory sinus arrhythmia (RSA) is known to decrease with advancing age, the independent effects of age, gender, conditioning status and body composition on RSA are unknown. The impact of age, fitness, gende and relative weight on resting RSA was examined in 117 healthy normotensive adults ages 19-82 from the BLSA; RSA was extracted from a 3-minute seated ECG using time domain digital filtering. By linear regression analysis, RS varied inversely with age (r = -0.60, p <.001) and body mass index (r = - 0.28, p <.01), directly with VO2max (r = 0.38, p <.001) and was unrelated t gender. Multiple regression analysis demonstrated that age and body mass but not VO2max were independent predictors of RSA. C. To examine the hypothesis that heart rate variability (HRV) is reduced in apparently healthy subjects with latent coronary artery disease (CAD), we measured resting ECG R-R interval variations in 29 asymptomatic male volunteers aged 61.8q11.2 years, free of clinical heart disease, who developed a coronary event (CE), within the next 2 years. Compared to 58 age-matched controls (C) who remained event free for 12.7q6.5 years after the index ECG, men destined for a CE showed smaller standard deviation of R-R (26.1 q 10.8 vs 37.9 q 24.0 msec, p = .002) and smaller absolute difference between minimum and maximum R-R interval (98.6 q 40.3 vs 136.7 q 81.0 msec, p = .004) indicating reduced HRV in men with latent CAD.